1. Field of the Invention
This invention relates to a roller type one-way clutch for use as a part of torque transmission, back stop or the like, for example, in the driving apparatus of an automobile, an industrial machine or the like, and more particularly to an improvement in a roller for the roller type one-way clutch.
2. Related Background Art
Generally, a roller type one-way clutch comprises an outer ring, an inner ring disposed concentrically with the outer ring, a plurality of rollers disposed between the outer peripheral surface of the inner ring and the inner peripheral cam surface of the outer ring for transmitting torque, a pad bearing having a U-shaped cross section for effecting the centering of the outer ring and the inner ring and also, guiding the rollers, a spring being in contact with the idle rotation side of the rollers, a mounting plate for the spring, etc.
In such a construction, the one-way clutch is designed such that the inner ring is rotated only in one direction relative to the outer ring by a cam mechanism comprised of a roller and a cam surface. That is, the inner ring is idly rotated in one direction relative to the outer ring, and gives rotational torque to the outer ring only in a direction opposite thereto through the cam mechanism.
A conventional roller will be described here with reference to FIG. 6 of the accompanying drawings. The conventional roller 100 has the shape of a cylindrical runner, and the rolling surface 101 of the roller 100 is of such an even straight shape as shown in Japanese Patent Application Laid-Open No. 8-338450. That is, the roller 100 is in contact with the inner ring or the outer ring over the entire surface thereof in the circumferential direction thereof.
However, when for example, the one-way clutch is used under a very low temperature environment (−20° C. to −40° C.) and the viscosity of ATF in an automatic transmission becomes high, it may happen that the roller type one-way clutch does not normally mesh during meshing engagement from idle rotation, but continuously slips. This leads to the problem that the meshing side of the roller type one-way clutch does not normally function.
For the roller type one-way clutch to mesh, the oil film between the roller and a raceway surface during idle rotation must be sheared and metals must completely contact with each other, but under a very low temperature, there has been the undesirable possibility that the roller continues to slip on the oil (ATF) made high in viscosity. This is because the oil film cannot be cut by the roller.